The field of the invention is earth grading and soil compaction, and the invention relates more particularly to tractors and other off-road equipment used for moving and compacting soil in preparation for construction.
Soil compaction is the process of physically densifying or packing the soil so that the soil is capable of supporting increased weight. It is generally accepted that the strength of a soil can be increased by densification, and three important factors affect compaction. These are material gradation, moisture content and compactive effort. Material gradation refers to the distribution o different particle sizes within a soil sample. A soil sample having particles of all one size would be said to be poorly graded. Such poorly graded soil cannot be effectively compacted. If, instead, the soil particles are of many different sizes, it will compact more easily since the smaller particles tend to fill the empty spaces between the larger particles leaving fewer voids after compaction.
Another important factor affecting soil compaction is moisture content. Water lubricates soil particles thus helping them slide into the most dense position Water also creates clay particle bonding giving cohesive materials their sticky qualities. It is very difficult, if not impossible, to achieve proper compaction in materials that are too dry or too wet. Soil experts have determined that in practically every soil there is an amount of water called the optimum moisture content at which it is possible to obtain maximum density with a given amount of compactive effort.
The last factor is compactive effort which may be from static weight or pressure from a kneading action, impact or vibration.
In large-scale earth moving projects, different pieces of equipment are utilized for the steps of mixing the soil to provide proper material gradation, for adding water and for compacting. For smaller projects, such large-scale equipment is too expensive and too unwieldy. For instance, the conversion of a former filling station lot to a strip center would not provide space to utilize the above-referenced large-scale equipment. Thus, smaller pieces of equipment such as a wheel loader is commonly used. A wheel loader has a front-mounted bucket which may be used to mix the soil to improve the gradation of the soil materials. Typically, in order to provide sufficient moisture contact, a worker with a garden or fire hose will wet the surface of the lot to be graded and will periodically add water as directed. The wheels of the loader will then be used for compaction together with the bucket for mixing and grading to provide a satisfactory degree of material gradation, moisture content and compactive effort.
It is inefficient, however, for a separate workman to simply operate a garden or fire hose for watering, and also the water is not evenly mixed in the soil when it is initially sprayed on the surface. Furthermore, the weight of the loader's wheels are often insufficient to provide the optimum in compaction. There is, thus, a need for a more efficient and more effective vehicle for grading, adding moisture and compacting soil.